Poly(vinylchloride) (PVC) plastisols (which typically consist of a mixture of poly(vinyl chloride) powder, plasticizers, fillers, and additives) are widely used as automotive seam sealers or protective underbody coatings. They are generally cured at 140.degree. C. or higher but often do not adhere well to electrodeposition coatings (E coats).
Polyamidoamines have been described in the prior art to serve as excellent adhesion improvers for PVC plastisols on various substrates. The development of polyamidoamine adhesion promoters for PVC plastisols and their uses in conjunction with or as adducts with epoxies, isocyanates, or Schiff's bases have been the subjects of several patents: U.S. Pat. No. 4,146,520 (1979); U.S. Pat. No. 4,440,900 (1984); U.S. Pat. No. 4,533,524 (1985); and U.S. Pat. No. 4,673,710 (1980).
At cure temperatures of 140.degree. C. or higher, the polyamidoamines can generally be added at low concentration (typically less than 0.5 weight percent) to achieve both adhesion and wet-on-wet paintability without any paint tack. However, at lower cure temperatures, i.e., 120.degree. C. or lower, a higher level of the polyamidoamine adhesion promoter is needed to achieve adhesion. This, however, tends to lead to a significant degree of paint tack due to incomplete paint curing on the plastisol surface. The paint tackiness is attributed to the complexation of the acid catalysts commonly used in high solids, enamel paints with the basic polyamidoamine adhesion promoters which subsequently deactivate the acid catalysts in the paints.
Other materials have also been described in the literature as adhesion improvers for PVC plastisols. U.S. Pat. No. 4,151,317 cited the use of adducts of Schiff's bases with diisocyanates as adhesion promoters for PVC plastisols. The use of silane compounds has also been reported as adhesion improvers for PVC plastisols such as in U.S. Pat. No. 4,268,548 and U.S. Pat. No. 4,540,731. However, these materials are generally basic and hence cannot be used with the acid catalyzed, high solids, enamel paints.
Diligent attempts have been made in recent years to develop PVC plastisol compositions curable at 120.degree. C. or lower while retaining good adhesion properties and wet-on-wet paintability. The reasons are twofold: (a) energy savings at 120.degree. C. cure as compared to 140.degree. C.; and (b) the conversion to acid catalyzed, high solids enamel paints cure at 120.degree. C. or lower in the automotive industry. Accordingly, there is a definite demand for PVC plastisols that can be painted wet-on-wet with these new paints and then cured at 120.degree. C. or lower to result in a good non-tacky paint finish while retaining good adhesion to the substrate. The PVC plastisol compositions described in the present invention meet these requirements.
Chem. Abs. 68 (4):13705n, "Poly(vinyl chloride) Plastisols," (Matsubara), discloses epoxidized plasticizers for chloroethylene polymers, crosslinked with isobutyric anhydride and methylsuccinic anhydride and methylsuccinic anhydride for mechanical improvement.
Chem Abs. 78 (16):98554s, "Fluidizing Agents for Plastisols," (Szilagyi and Arfiche), describes a mixture of PVC plastisol, dioctyl phthalate and tetrapropenyl succinic anhydride with "improved heat stability and low viscosity."
Chem. Abs. 92 (4):23407b, "Setting of Epoxy Resins by Complexes based on Maleic Anhydride and N-Vinyl Monomers," (Vashevko et al.), describes a complex of maleic anhydride with N-vinyl succinimide, used in thermosetting compositions of epoxy resins. It was claimed that resin viscosity was reduced and storage life increased from 24 hours to 30 days.
Chem. Abs. 101 (8): 56095f, "Vinyl Chloride Polymer Plastisols," (Eroskey) describes PVC plastisol with "small amounts of epoxy resins and anhydride curing agents" for good abrasion resistance.
Chem Abs. 105 (2): 8054c, "Chemical Strengthening of Plastisols" (Krejci, et al.) describes PVC plastisols modified with isophorone diamine, methyltetrahydrophthalic anhydride and 3 percent epoxy resin.
Several patents describe various adhesion promoters or improvers for PVC plastisols (some have already been noted):
U.S. Pat. No. 4,146,520, Bierworth et al (1979), a polymerized fatty acid plus polyalkylene amine.
U.S. Pat. No. 4,151,317, Burba et al (1979), adduct formed between an isocyanate and a Schiff base.
U.S. Pat. No. 4,268,548, Burba et al (1981), azomethine/silane compound.
U.S. Pat. No. 4,440,900, Burba et al (1984), condensation product of a polymerized fatty acid, a polycarboxylic acid, and a polyalkylene polyamine.
U.S. Pat. No. 4,673,710, Burba et al (1987), condensation product formed between a polyaminoamide and a carboxylic acid or ester.
European Pat. Appln. EP 171850 (1986) describes polyaminoamide adhesion promoters made from polymerized unsaturated fatty acids and piperazine.
However, none of the above articles describe the particular use of epoxy resin and acid anhydride with PVC plastisols as a coating on anything, and indeed, not to enhance the adhesion of PVC to electrodeposition coatings, and of course not to affect wet-on-wet paintability with high solids, enamel paints or to produce 40.degree. C. storage stable compositions with the addition of an imide. In this invention, the properties mentioned above have been attained.